Cryogenic storage container



April 30, 1968 H. E. BROUGHAM ET AL 3,330,611

CRYOGENIC STORAGE CONTAINER Filed April 25, 1966 II/lll/I/l/III/IIl/l/TI775 firl/l/l/ /j//// /////////////////////I/ll/R Z-Tb I FIG I h 9 8b 5 L A 1 1 j H 5 n E k I HAROLD E. BROUGHAM JAMES J. GILCHRIST INVENTORS sYg/wzim ATTORNEY United States Patent 3,380,611 CRYOGENIC STORAGE CONTAINER Harold E. Brougham, Arlington, and James J. Gilchrist, Irving, Tex., assignors to LTV Aerospace Corporation, Dallas, Tex., a corporation of Delaware Filed Apr. 25, 1966, Ser. No. 544,996 13 Claims. (Cl. 220-1) This invention relates to apparatus for storing lowtemperature liquids with little heat-leak evaporation and more particularly to a container supported by a lightweight structure with a low heat-leak coefiicient.

The demand for cryogenic storage containers and transport trailers has expanded in the last few years as their use in space vehicles and industry has increased. Cryogenic storage containers are constructed in many configurations, such as cylindrical, spherical, conical, and combinations of these. Although the present invention was perfected as a spherically shaped container, it can be used with any of the previously mentioned designs. The spherically shaped containers do, however, have a very important advantage because of an inherently low shell thickness and surface area per unit of volume.

The cost of maintaining a given quantity of liquified gas at a predetermined temperature is directly related to the amount of heat leakage to the stored gas. Thus, when designing a tank support for a cryogenic container, it is essential that the heat-leak contribution of the support be reduced to a minimum. This invention provides a support structure for a tank containing liquified gas that reduces the heat-flow contribution by the support to its minimum value.

Difficulties encountered in storing liquified gases, such as hydrogen, nitrogen, or helium, at near absolute-zero conditions have resulted in a re-evaluation of container supporting structures. The storage tank itself is well insulated to reduce to the barest minimum the amount of heat leakage to the interior of the tank; but the supporting structures have, in the past, caused excessive amounts of heat leakage. Thus, the tank support structure has materially increased the energy input, and consequently the cost, due to boil-off of the liquid gas, of maintaining the liquified gases at very low temperatures. Heretofore, various designs have been proposed to support the cryogenic containers; many of these earlier designs used What is known as a point-contact support. In essence, such a design employs a plurality of supporting legs distributed at various locations around the container. Due to the nature of such supports, the stresses developed in the container are concentrated at localized areas. This results in an overall tank design that is necessarily of heavier construction for it to be capable of withstanding the highly localized areas of stress. It also results in uneven expansion of the tank during changing temperature conditions. Some tank support structures did provide for tank eX- pansion using a ring design that cradled the container; they did not, however, contribute significantly to reducing the heat leak to the super-cold, liquified gas.

In the practice of the present invention, there is provided a tank support in the shape of a frustum of a cone. To reduced the heat leak to a minimum, a material of low thermal conductivity, such as a glass-reinforced resin, is used for the support. The cryogenic container is mounted on top of the frustum-shaped support and is free to expand and contract without stressing small localized areas. The tank itself need only be strong enough to contain the liquified gas.

An object of the invention is to provide a support with a low heat-leak coeflicient for a container of low-temperature, liquified gases.

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Another object of the invention is to provide a lightweight support for a container of lowtemperature, liquified gases.

A further object of the invention is to provide a light- Weight support having a low heat-leak coeflicient for a container of low-temperature, liquified gas.

A still further object of the invention is to provide a low heat-leak support for a spherically shaped container of low-temperature, liquified hydrogen gas, which support eliminates localized stress areas.

Another object of the invention is to provide a hanging support structure, of a material of low thermal conductivity, for supporting a container of low-temperature, liquified gas.

Other objects and advantages will be apparent from the following description of a preferred embodiment of the invention and as particularly pointed out in the appended claims and in view of the drawing, wherein:

FIG. 1 is a somewhat schematic, elevational view of a frustum-shaped support structure for a spherical tank capable of storing a low-temperature, liquified gas with little heat leakage.

FIG. 1A is a cross-sectional view of a portion of the tank and support zone and showing the mating relationship between the zone and the support frame, also shown in section.

FIG. 1B is a cross-section of the corrugated lower edge of the frustum-shaped support, taken as at line 1B-1B of FIG. 1.

FIG. 1C is a cross-section of the corrugated frustumshaped support, taken along line 1C1C of FIG. 1.

FIG. 1D is a cross-section of a portion of the base frame.

FIG. 2 is a somewhat schematic, elevational View of an inverted frustum-shaped support structure for effecting support, with a minimum of heat leakage, of a tank containing a low-temperature, liquified gas.

FIG 2A is a cross-section of the hanging support bracket for the structure of FIG. 2, taken as at line 2A-2A of FIG. 2.

Referring to FIG. 1, there is shown a spherical storage tank 1 for storing liquified gas at temperatures in the neighborhood of zero degrees Kelvin (273 C.). Because of the somewhat violent reactions that can occur in the storage of liquified gases, the selection of structural materials for the tank 1 is usually limited to the face centered cubic metals and alloys, such as aluminum, copper, nickel, their alloys, and the austenitic stainless steel. Included as an integral part of the tank 1 is a support zone 2, defined at the container surface by passing two imaginary, parallel planes through the container at right angles to its vertical centerline and below the c'ontainers horizontal diameter. Preferably, the support zone 2 will be of the same material as the remainder of the tank.

The heat leakage to a container for storing liquified gases is measured by the quantity of heat per unit of time that penetrates the container via the insulating material, the tank support structure, and the necessary connecting piping. The result of this heat transfer is a. partial evaporation of the super-cold liquid and is referred to as the heat-leak evaporation rate. There are many insulating techniques for reducing the heat-leak through the tank itself. They are generally classified according to the type of method of insulation, and the more common are:

(l) Vessels insulated with rigid-cellular or fiber insulation. (2) High-vacuum insulated vessels.

(3) Evacuated-powder and evacuated-fiber insulated vessels.

(4) Evacuated multiple-radiation-shield insulated vessels.

Techniques for insulating the container itself have been perfected to the point where the predominant source of heat transport is the support structure.

In FIG. 1, the spherical storage tank 1 is supported by a frustum-shaped structure 4 in contact with the tank at the support zone 2. In some applications, especially in space vehicles, it is advantageous to design the frustumshaped structure 4 to have the apex of the cone-shaped figure of which it is a part coincide with the center of the spherical storage tank 1. However, two other factors for reducing the heat leak must be taken into consideration: (1) the longer the frustum, the lower the heat leak, and (2) the smaller the supporting circle, the lower the heat-leak. The amount of heat transfer contributed by the support structure 4 to the stored liquid can be computed using the following equation:

KA q r- 1) where q=heat transfer per unit of time k=average thermal conductivity of the support between T2 and T1 A =cross-sectional area of the support T =temperature at the hot end of the support T =temperature at the tank surface x-=length of support member The best materials for the support structure 4 are those that have good tensile and/ or compression strength and a low thermal conductivity. In selecting the material to be used, a good index of comparison is the ratio of its strength to thermal conductivity. Materials with a high ratio are preferred; some of the better materials are glassreinforced plastics, polyethylene terephthalate, and synthetic polyamide. A glass fiber and resin laminate was used in the perfection of the present invention, since it exhibited particularly advantageous properties.

Another important feature of the invention is the corrugated design of the support structure 4. Corrugating the support eliminates two troublesome problems found in prior tank supports: one, it provides a support with low cross-sectional area and a distributed support configuration; two, it allows expansion of the tank without stressing the support itself. Considering the first problem, as mentioned previously, a point-contact design localizes the stress areas and requires an extra-heavy tank construction. Using a fiat (i.e., noncorrugated), frustumshaped design is inefficient compared to the approach described herein because, to provide the necessary structural stability to a flat-surfaced, frustum-shaped support, additional mass would be required, thus increasing the cross-sectional area and, hence, the quantity of heat transferred to the stored super-cold liquid. The second problem solved by the use fo a corrugated design is possibly of still greater importance than the first. As the storage tank 1 expands or contracts, the corrugations change shape with very little if any additional stress in either the tank or the support. It should be noted that these advantages can only be gained if the corrugations extend in a direction from the apex of the cone to its base.

FIGS. 1B and 1C show the corrugation configuration of the lower and upper edges of the support structure 4. FIG. 1B shows the corrugations of the support structures lower edge, which is attached by means of rivets 7a, 7b to a U-shaped frame 6 shown in cross-section in FIG. 1D. Specificially, the U-shaped frame 6 is of a circular design, with the circle diameter slightly larger than the diameter of the storage tank 1 and with a flat supporting surface. There are no special requirements as to the material from which the frame 6 should be made. It may be attached to a main support structure such as a concrete base in ground applications or the super-structure of a space vehicle in space applications. The base frame 6 merely serves to maintain the desired shape of the support structure 4. Referring to FIG. 1D, there is shown a cross-sectional view of the frame 6 with the support 4 riveted in place by means of rivets 7a, 712. Two important features of this connection that materially reduce the heat leak to the tank 1 are the line-contact between the support and the frame at each corrugation, and the spacing between the supports lower edge 20 and the closed base 25 of the frame 6.

Referring to FIG. 10, there is shown the attachment of the corrugations of the supports upper edge, by means of rivets 8a, 8b, to a U-shaped upper frame 9, shown in cross section in FIG. 1A. The upper edge 21 (FIG. 1A) of the support 4 is spaced from the closed base 26 of the frame 9 and the contact between the support and the frame is a line at the peak of each corrugation. This is similar to the construction at the supports lower edge and also materially reduces the heat leak to the tank 1. The U-shaped frame 9 is of a circular shape and mates with and is the complement of the support zone 2. Preferably, the U-frame 9 is of the same material as that of the tank and can be formed as a part of the tank itself although this is not a prerequisite. Dimensionally, the edge length of a corrugation in the upper frame 9, between rivets 8a, 8b (FIG. 1C) is equal to the edge length of a corrugation in the lower holder 6, between rivets 7a and 71') (FIG. 13). With equal edge-length corrugations at the upper and lower edges of the support structrue 4, the linear dimensions of the upper and lower edges will be equal. Although this does not contribute significantly to the operating advantages of the support, it does simplify the design and manufacture and results in a uniform stress level in the support.

In FIG. 1, the corrugated, frustum-shaped support is shown in an application where it is in compression; it may also be used in tension to support a hanging tank. Referring to FIG. 2, there is shown a spherical storage tank 11 for storing a super-cold, liquified gas, such as liquid oxygen. For space applications, the spherical tank 11 can be covered with superinsulation and a bag made from polyethylene terephthalene to minimize the heat leakage to the stored fluid. One of the sophisticated insulating schemes described with reference to FIG. 1 would not be required in the vacuum existing in space. Supporting the spherical tank 11 is a suspension hanger 12. This hanger 12 has a curved, elongated portion 23 shaped to complement the surface of the tank 11 against which it rests and, at its upper end, a U-shaped portion with upstanding legs and a closed lower end. Attached to the suspension hanger 12 is an inverted, corrugated, frusturn-shaped support structure 14. The support structre 14 is riveted to a channel-shaped ring frame 16 and the suspension hanger 12.

Referring to FIG. 2A, it will be noted that the lower edge 22 of the support structure 14 is not in contact with the closed lower end of the suspension hanger 12. The only physical contact between the support structure .14 and the suspension hanger 12 is at the peaks of the corrugations where attached by the rivets 18. As was explained previously, this further reduces the heat-leakage contributed by the support structure, for the heatflow is restricted to a line contact. The important features of the frustum-shaped support of FIG. 1 are found in the inverted frustum-shaped support 14 of FIG. 2. That is, the tank support contributes little to the total heat leakage, provides a distributed load-path instead of a poincontact design, and induces little local stress due to temperature expansion of the storage tank.

Storing liquified gas at very low temperatures is important in stationary as well as mobile applications. In mobile systems, in addition to the heat leakage and expansion problems, forces of acceleration must be considered. The use of lightweight, low thermal conductivity material, such as a glass reinforced plastic, makes our support structure ideal for both mobile and stationary systems. Our corrugated design increases the rigidity of the fiberglass material and reduces the overall weight of the mobile system.

While several embodiments of the invention, together with modifications thereof, have been described in detail herein and shown in the accompanying drawings, it will be evident that various further modifications are possible in the arrangement and construction of its components without departing from the scope of the invention.

We claim:

1. Apparatus for storing low-temperature liquids, comprising:

an insulated container for storing low-temperature liquids under conditions of low heat-induced evaporation thereof and having a support-zone area defined at its surface by two, imaginary, parallel planes through the container at right angles to a centerline of the container;

an upper support frame having a container-supporting surface in mating contact with and the complement of the container support-zone;

a base frame with a flat supporting surface and having an outline similar to that of the upper support frame; and

support means of a low thermal conductivity material having corrugations that extend along the axes of the supporting forces and having a contour for connection to the upper and base frames at each corrugation peak in a manner that provides a low heat leakage path from the container to the base frame and provides a means for supporting said container.

2. Apparatus for storing low-temperature liquids as set forth in claim 1 wherein the corrugated, low thermal conductivity material of the support means is a glass-reinforced resin.

3. Apparatus for storing low-temperature liquids, comprising:

an insulated, spherical container for storing low-temperature liquids under conditions of low heat-induced evaporation thereof and having a support-zone area encircling the sphere below its great-circle diameter and defined at its surface by two, imaginary, parallel planes through the container at right angles to its vertical centerline;

an upper support frame having a container-supporting surface in mating contact with and the complement of the container-supporting zone;

a ring-shaped base frame with a fiat supporting surface; and

support means of a low thermal conductivity material having corrugations that extend along the axes of the supporting forces and having a contour for connection to the upper and base frames at each corrugation peak in a manner that provides a low heat leakage path from the container to the base frame and provides a means for supporting said container.

4. Apparatus for storing low-temperature liquids as set forth in claim 3 wherein the upper and bases frame are of U-shaped radical cross-section and the support means is fastened within the U-shaped frames, each of the U-shaped frames having a closed base.

5. Apparatus for storing low-temperature liquids as set forth in claim 4 wherein the corrugation peaks of the support means are fastened to the U-shaped frames and the support edges are spaced from the closed bases of the U-shaped frames.

6. Apparatus for storing low-temperature liquids as set forth in claim 3 wherein the diameter of the ring-shaped base is greater than the spherical container diameter.

7. Apparatus for storing low-temperature liquids as set forth in claim 6 wherein the support means is frustumshaped.

8. Apparatus for storing low-temperature liquids as set forth in claim 7 wherein the low thermal conductivity material of the support means is laminated, glass-reinforced resin.

9. Apparatus for storing low-temperature liquids as set forth in claim 8 wherein the axes of the supporting forces meet at a point which coincides with the center of the spherical container.

10. Apparatus for storing low-temperature liquids as set forth in claim 9 wherein the low thermal conductivity material of the frustum-shaped support means is a laminated, glass-reinforced resin.

11. Apparatus for storing low-temperature liquids, comprising:

a superinsulated, aluminum, spherical container for storing low-temperature liquids under conditions of low heat-leakage induced evaporation and having a support-zone encircling the sphere below the horizontal diameter and defined at its surface by two imaginary, parallel planes through the spherical container at right angles to the vertical centerline thereof;

an upper support frame of a U-shaped radial crosssection having a closed base, the upper support frame having a container-supporting surface in mating contact with and the complement of the container support-zone; a circular base support of a U-shaped radial cross-section having a closed base, the base support having a fiat supporting surface; and

a frustum-shaped support means of a low thermal conductivity material having corrugations that extend in the direction of the axes of the supporting forces within the supporting means and that are fastened to the upper support frame and base support at the corrugation peaks, With the edges of the frustumshaped support means being spaced from the closed bases of both the upper support frame and the circular base support.

12. Apparatus for storing low-temperature liquids as set forth in claim 11 wherein the frustum-shaped support is in compression and the spherical container is mounted on top of the support.

13. Apparatus for storing low-temperature liquids as set forth in claim 11 wherein the frustum-shaped support is in tension and the spherical container hangs by means of the circular base support.

References Cited UNITED STATES PATENTS 1,918,335 7/1933 Heylandt 2209 1,979,224 10/1934 Hansen et al. 2209 2,562,601 7/1951 Caquot et al 22 0-18 2,672,254 3/ 1954 Boardman 22069 3,152,713 10/1964 Clifford 22015 THERON E. CONDON, Primary Examiner.

J. R. GARRETT, Assistant Examiner. 

1. APPARATUS FOR STORING LOW-TEMPERATURE LIQUIDS, COMPRISING: AN INSULATED CONTAINER FOR STORING LOW-TEMPERATURE LIQUIDS UNDER CONDITIONS OF LOW HEAT-INDUCED EVAPORATION THEREOF AND HAVING A SUPPORT-ZONE AREA DEFINED AT ITS SURFACE BY TWO, IMAGINARY, PARALLEL PLANES THROUGH THE CONTAINER AT RIGHT ANGLES TO A CENTERLINE OF THE CONTAINER; AN UPPER SUPPORT FRAME HAVING A CONTAINER-SUPPORTING SURFACE IN MATING CONTACT WITH AND THE COMPLEMENT OF THE CONTAINER SUPPORT-ZONE; A BASE FRAME WITH A FLAT SUPPORTING SURFACE AND HAVING AN OUTLINE SIMILAR TO THAT OF THE UPPER SUPPORT FRAME; AND SUPPORT MEANS OF A LOW THERMAL CONDUCTIVITY MATERIAL HAVING CORRUGATIONS THAT EXTEND ALONG THE AXES OF THE SUPPORTING FORCES AND HAVING A CONTOUR FOR CONNECTION TO THE UPPER AND BASE FRAMES AT EACH CORRUGATION PEAK IN A MANNER THAT PROVIDES A LOW HEAT LEAKAGE PATH FROM THE CONTAINER TO THE BASE FRAME AND PROVIDES A MEANS FOR SUPPORTING SAID CONTAINER. 